As both large windmills serving communities and smaller ones privately owned become numerous, provision for safe operation will be required to gain public acceptance. Large windmills employ control mechanisms with provisions for safe operation equivalent to those of steam turbines presently supplying most of our electrical energy. Many small windmills employ less effective means, such as blades designed to stall gradually or change blade angle thru a minimum angle by direct action of a speed governor, thereby limiting rotational speed to a safe maximum in normal wind conditions. But those are incapable of reducing aerodynamic forces on the blades to near zero, by rotating them into alignment with the wind, as do the controls of large windmills.
Hydraulic control systems can rotate windmill blades to a safe full-feathered position under normal control, and, by careful design, spring force can be provided to make the control fail-safe if the hydraulic mechanism should break down. Existing hydraulic control systems employ separate mechanical elements to sense speed, supply hydraulic fluid, and to control blade angle. Mountings of these separate elements, connecting levers, and pipe connections are costly and are subject to failure. Also, an enclosure is usually required to protect them from weather.
This invention discloses a cost-effective hydraulic windmill control system, using the main windmill shaft as a cylinder for a piston to feather the blades, and using a torsion spring within each blade to provide feathering forces. The main shaft also carries a governor sensitive to shaft speed and which controls piston position by using a short travel dump valve and piston hydraulic pressure as a feedback signal proportional to piston position to control blade pitch. Fluid connection between piston, governor dump valve, and the pump are thru-passages machined in the shaft. The pump supplies fluid in quantities proportional to shaft speed, and, in the arrangement described, is driven by an eccentric on the main shaft. This pump has two separate pumping displacements, both together supplying sufficient fluid quantities to assure rotation of the blades from full-feathered position at low idling windmill speed. A suction valve having a large starting displacement is held open when the operating piston has moved thru approximately half stroke. A smaller displacement then supplies fluid for normal operation requiring minimum shaft torque to run the pump.
All elements of the control system, and gears driving a generator loading to windmill, are enclosed in an oil tight housing. A dump valve provides means of shutdown to full-feathered blade position by signals related to vibration, overspeed, manual control and others. A shutdown actuated by high wind velocity is cancelled automatically when winds diminish. The housing serves as a reservoir for hydraulic fluid, and a lower cylindrical part holds bearings which permit the windmill to rotate on a tower in response to changes in wind direction. A tight housing cover provides access for maintenance of the control system.